The term Diet of Speyer refers to any of several sessions of the Diet of the Holy Roman Empire when it chose to meet in the city of Speyer, Germany. The most famous sessions occurred in 1526 and 1529.

1526 Diet of Speyer

The major decision of this Diet was that, until a General Council could meet and settle the theological issues raised by Martin Luther, the Edict of Worms would not be enforced and each Prince could decide if Lutheran teachings and worship would be allowed in his territories (Cuius regio, eius religio).

1529 Diet of Speyer

Ascendent Roman Catholic forces prevailed to reverse the policy of religous tolerance adopted in 1526. The Edict of Worms was to be enforced after all, without waiting for a General Council. This was opposed by members that supported Lutheran teachings and practices, who vigorously protested the decision. Their action created the term Protestantism still used today as a name for this religious movement.

1542 Diet of Speyer

1544 Diet of Speyer

1570 Diet of Speyer